linux-kernel - Re: [PATCH v2 2/2] perf jevents: Autogenerate empty-pmu-events.c

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Date: Tue, 28 May 2024 08:14:14 -0700
From: Ian Rogers <irogers@...gle.com>
To: John Garry <john.g.garry@...cle.com>
Cc: Weilin Wang <weilin.wang@...el.com>, Peter Zijlstra <peterz@...radead.org>, 
	Ingo Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Adrian Hunter <adrian.hunter@...el.com>, Kan Liang <kan.liang@...ux.intel.com>, 
	Jing Zhang <renyu.zj@...ux.alibaba.com>, Sandipan Das <sandipan.das@....com>, 
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] perf jevents: Autogenerate empty-pmu-events.c

On Tue, May 28, 2024 at 3:01 AM John Garry <john.g.garry@...cle.com> wrote:
>
> On 25/05/2024 02:30, Ian Rogers wrote:
> > empty-pmu-events.c exists so that builds may occur without python
> > being installed on a system. > Manually updating empty-pmu-events.c to
> > be in sync with jevents.py is a pain, let's use jevents.py to generate
> > empty-pmu-events.c.
> >
> > 1) change jevents.py so that an arch and model of none cause
> >     generation of a pmu-events.c without any json. Add a SPDX and
> >     autogenerated warning to the start of the file.
> >
> > 2) change Build so that if a generated pmu-events.c for arch none and
> >     model none doesn't match empty-pmu-events.c the build fails with a
> >     cat of the differences. Update Makefile.perf to clean up the files
> >     used for this.
> >
> > 3) update empty-pmu-events.c to match the output of jevents.py with
> >     arch and mode of none.
> >
> > Signed-off-by: Ian Rogers <irogers@...gle.com>
>
>
> Reviewed-by: John Garry <john.g.garry@...cle.com>

Thanks!

> > ---
> >   tools/perf/Makefile.perf                 |   2 +
> >   tools/perf/pmu-events/Build              |  12 +-
> >   tools/perf/pmu-events/empty-pmu-events.c | 894 ++++++++++++++---------
> >   tools/perf/pmu-events/jevents.py         |   6 +-
> >   4 files changed, 562 insertions(+), 352 deletions(-)
> >
> > diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.per
>
> ...
>
> > -     },
> > +struct pmu_table_entry {
> > +        const struct compact_pmu_event *entries;
> > +        uint32_t num_entries;
> > +        struct compact_pmu_event pmu_name;
> > +};
> > +
> > +static const char *const big_c_string =
> > +/* offset=0 */ "default_core\000"
> > +/* offset=13 */ "bp_l1_btb_correct\000branch\000L1 BTB Correction\000event=0x8a\000\00000\000\000"
> > +/* offset=72 */ "bp_l2_btb_correct\000branch\000L2 BTB Correction\000event=0x8b\000\00000\000\000"
>
> Please remind me: how to figure out this number when adding a new entry?

So this shouldn't be generated by hand. The old one was, this one is
created by jevents.py as maintaining something by hand is a pain. If
you need to add entries then they are in the
`tools/perf/pmu-events/arch/test/` directory. When you build with
NO_JEVENTS=1 then this file will be used. When building normally
jevents.py will be used and used to check that the empty-pmu-events.c
isn't out-of-date - the build will break if it is. The fix is just to
copy `test-empty-pmu-events.c` to `empty-pmu-events.c`, which is
hopefully implied by the result of the diff being shown.

Thanks,
Ian

> > +/* offset=131 */ "l3_cache_rd\000cache\000L3 cache access, read\000event=0x40\000\00000\000Attributable Level 3 cache access, read\000"